A number of advances have been made in the fields of biotechnology and pharmaceutical research to increase the speed and accuracy of analytical operations. In at least one major advancement, technologies developed for the semiconductor industry have been adapted to manufacture miniaturized integrated devices that can be used to perform analytical operations much more quickly, with much greater accuracy, and with less operator involvement. These microfluidic devices have been commercially adapted for genetic and protein analysis in the form of the Agilent 2100 Bioanalyzer and associated LabChip® microfluidic devices and reagents developed by Caliper Life Sciences, Inc. Other commercial applications for microfluidic devices and systems are in the pharmaceutical industry where they are used in ultra high-throughput screening analysis. These systems allow large numbers of different pharmaceutical candidate compounds to be screened against target assays in relatively short amounts of time, to determine whether any of those compounds possess desirable pharmacological activity. The resulting assays give improved data quality and increased automation, while minimizing the amounts of potentially very expensive reagents.
While microfluidic systems have been shown to improve the speed and accuracy of screening assays, there are a number of areas where the small size and enhanced speed of these systems can be a handicap to a screening assay. This is the case, for example, where a particular analyte is at a very low concentration in the fluid that is being tested. In such instances, the small volumes of the fluid that are present in a detection region of a microfluidic device may contain only a few hundred molecules of interest. In such cases, the amount of material present may fall below the detection level of the particular system that is being employed. Similarly, for assays that progress at relatively slow rates, the speed of operation of microfluidic systems may cause some difficulty in yielding enough product of the reaction so that it can be readily and accurately detected. The present invention provides some solutions for these problems, as well as others that may be faced in microfluidic and other analytical systems.